Substrates that are mainly used in fabrication of very large scale integrated semiconductor devices are silicon wafers with mirror-polished surfaces that are made from silicon single crystal grown by the CZ method. As the diameter of silicon wafers are enlarged to reduce fabrication cost of semiconductor devices, apparatus for manufacturing a single crystal and components in its furnace become increasingly larger.
An exemplary apparatus for manufacturing a single crystal according to the CZ method that is conventionally used, for example, in manufacture of semiconductor silicon single crystals will now be described with reference to FIG. 4.
As shown in FIG. 4, the apparatus 101 for manufacturing a single crystal includes a main chamber (a pulling chamber) 102, a crucible 103 accommodated in the main chamber 102, a cylindrical heater 104 disposed so as to surround the crucible 103, a crucible holding shaft 105 and its rotation mechanism (not shown) for rotating the crucible 103, a seed chuck 107 for holding a silicon seed crystal 106, a wire 108 for pulling the seed chuck 107, and a winding mechanism (not shown) for rotating or winding the wire 108.
The crucible 103 is composed of a quartz crucible disposed on the inside on which a raw material melt (herein, a silicon melt) 109 is received and a graphite crucible disposed on the outside. A heat-insulating material 110 is disposed around the outside of the cylindrical heater 104. A heat-insulating plate 111 is disposed at a bottom portion.
Next, a method for growing a single crystal with the above apparatus 101 for manufacturing a single crystal will be described.
A polycrystalline silicon raw material with high purity is first heated to a melting point (about 1420° C.) or more in the crucible 103 and melted. The wire 108 is then reeled out such that the tip of the seed crystal 106 is brought into contact with or dipped into the melt at substantially the center of the melt surface. After that, while the crucible holding shaft 105 are rotated in the appropriate direction, the wire 108 is reeled up with the wire rotated to pull the seed crystal 106. The growth of the single crystal begins with this procedure. The pulling rate and temperature are thereafter adjusted appropriately, so that a single crystal ingot 112 having a substantially cylindrical shape can be obtained.
The above quartz crucible and graphite crucible in the apparatus 101 for manufacturing a single crystal both have high heat resistance, but the disadvantage in that the crucibles are comparatively brittle and lacking in impact resistance. When a single crystal is pulled, accordingly, the crucible 103, in some cases, is cracked due to the impact caused when a polycrystalline raw material is introduced into the crucible 103, and the raw material melt 109 leaks therefrom.
In addition, in some cases, the melt in the crucible 103 is splashed around the crucible 103 upon the introduction of the polycrystalline raw material. When the crucible 103 deteriorates gradually through use or the single crystal 112 falls down during pulling, there is a risk of leak of substantially the entire melt due to damage to the crucible 103.
In view of these, a single-crystal pulling apparatus disclosed in Patent Document 1, for example, is provided with, at the bottom of the main chamber 102, a melt-leakage receiving tray 113 having a sufficient internal volume to contain the entire raw material melt.